1. Field of Invention
The present invention relates to visual processing devices, display devices, image-capturing devices, portable information devices, and integrated circuits, and in particular relates to visual processing devices, display devices, image-capturing devices, portable information devices, and integrated circuits in which the strength of visual processing of an image is changed.
2. Description of the Related Art
Spatial processing and tone processing (tone mapping processing) are known as methods for visually processing an image signal of an original image.
In spatial processing, a target pixel to be filtered is processed using the pixels surrounding the target pixel. Another method that is known is to use an image signal that has been spatially processed in order to perform contrast enhancement or dynamic range (hereinafter, abbreviated as “DR”) compression, for example, of the original image (for example, see Patent Document 1).
Tone processing is processing in which a lookup table (hereinafter, abbreviated as “LUT”) is used to effect pixel value conversion for each target pixel, regardless of the pixels surrounding that target pixel, and is also known as gamma correction. For example, to enhance the contrast, pixel value conversion is performed using a LUT for assigning a wide range of tone to frequently appearing tone levels (that cover a large area) in the original image. Some examples of tone processing in which a LUT is employed include tone processing in which a single LUT is selected and used for an entire original image (histogram equalization), and tone processing in which a LUT is selected and used for each of a plural number of image regions obtained by partitioning the original image (local histogram equalization).
Conventional visual processing devices have been provided with a plurality of profile data with different conversion characteristics, and achieved the different visual processing modes discussed above by switching the profile data (for example, see Patent Document 2).
FIG. 47 illustrates a conventional visual processing device 900. In FIG. 47, the visual processing device 900 is made of a spatial processing portion 901 that executes spatial processing on the luminance value of each pixel of an original image that has been obtained as an input signal IS and outputs an unsharp signal US, and a visual processing portion 902 that uses the input signal IS and the unsharp signal US for the same pixel to perform visual processing of the original image, and outputs an output signal OS. The unsharp signal US is the brightness signal of a local region in which the luminance signal has been processed by a low-pass filter, and is a blur signal. The visual processing portion 902 is constituted by a two-dimensional LUT.
The visual processing portion 902 executes gamma correction with the tone conversion characteristics shown in FIG. 48, and selects a tone conversion curve that corresponds to the unsharp signal US of a target region in the image in order to increase or decrease the contrast. For example, it selects the curve of unsharp signal USO to brighten dark regions in the image, whereas it selects the unsharp signal USn curve to inhibit brightness in bright regions and strengthen the contrast. This group of curves is called a profile.
A profile data registration device 903 is provided with profile groups for different types of visual processing, and in the visual processing portion 902 registers the most appropriate profile for a target visual processing.
The profile data registration device 903 also updates to required profile data according to the strength of the visual processing.
For example, when it was desirable to change the strength of contrast enhancement in dark regions between when a face is extremely dark and when it is slightly dark even in a backlit image, then the brightness was adjusted by updating to profile data that have the most appropriate tone conversion characteristics.
Patent Document 1: U.S. Pat. No. 4,667,304.
Patent Document 2: International Disclosure Pamphlet No. 2005/027043.